Hundreds of fishing tools have been devised over the years to retrieve a tool or tubular which is stuck in a well. In many applications, a wireline lowers the fishing tool into the well, and a grapple at the end of the tool engages the stuck tool or tubular. An upward force on the wireline may then be used to dislodge the tool. In other applications, hydraulically powered or mechanically powered jars are used to generate a jarring force to dislodge the stuck tool or tubular in a well. While many types of tools can be retrieved using the above techniques, more complicated and lengthy tools frequently cannot be reliably retrieved with the above techniques, or if retrieved cause significant damage to the stuck tool or to the components remaining in the well.
U.S. Pat. No. 5,070,941 discloses a downhole force generating tool with an anchor and a piston/cylinder arrangement. U.S. Pat. Nos. 5,228,507 and 5,398,753 disclose a wireline retrieving tool with an anchor and a force generating means, such as an electric motor generating power to operate a fluid motor and a hydraulic pump.
More recently, U.S. Pat. No. 7,051,810 discloses a force generating tool with a downhole power unit, an anchor, and a pulling tool. The power assembly may be self-contained, thereby eliminating the need to supply power from the surface.
U.S. Pat. No. 7,021,382 discloses an axial force generating tool with a housing and an outer seal between the housing and the borehole. A piston may be supplied with pressurized fluid to create the axial pulling force. U.S. Pat. No. 7,367,397 discloses an impact generator which includes a downhole power unit and a jarring tool.
The disadvantages of the prior art are overcome by the present invention, and an improved hydraulically powered fishing tool and a method of fishing a tool or tubular from a well are hereinafter disclosed.